The present invention relates to a wiring substrate, a semiconductor device, and a method for manufacturing a wiring substrate.
When mounting a component such as a semiconductor chip on a wiring substrate, an insulation material referred to as a solder resist protects the outermost layer of the wiring substrate from the adhesion or contamination of solder and the like. In this case, to form a pad that is required to couple the mounted component, the insulation material (solder resist) includes an opening, which exposes a wiring layer that is formed under the solder resist. The opening is formed by performing photolithography, screen printing, laser processing, or the like.
When performing photolithography, referring to FIG. 12(a), the necessary number of lower layer wires 14 and 15 are first formed on a core substrate 11. The lower layer wires 14 and 15 are respectively covered by insulation layers 12 and 13. Then, a wiring layer 80, which serves as an uppermost layer, and an insulation layer 81 (solder resist layer), which covers the wiring layer 80, are formed. Subsequently, photolithography is performed to expose and develop the insulation layer 81. This forms a predetermined pattern of openings 81a as shown in FIG. 12(b) and exposes parts of the wiring layer 80, which is the uppermost layer, as pads 80a. 
When performing screen printing, a printing mask is used to print insulation material (solder resist) in only the necessary portions. When performing laser processing, an insulation material (solder resist) is applied entirely to a surface. Then, a laser beam is emitted against regions that are to be exposed (regions corresponding to openings) in order to remove the insulation material.
As described above, in photolithography, photosensitive resin is used as the solder resist, and the solder resist is exposed and developed to form a pattern. However, the heat resistance and chemical resistance of a photosensitive resin are usually low. In screen printing and layer printing, non-photosensitive resin such as thermosetting resin that has a higher reliability than photosensitive resin can be used as the solder resist. However, the formation of fine patterns is difficult, and the manufacturing cost is high.
Blasting has also been proposed as another method for forming openings that expose pads. For example, when performing sandblasting, referring to FIG. 13(a), the necessary number of lower layer wires 14 and 15 are first formed on a core substrate 11. The lower layer wires 14 and 15 are respectively covered by insulation layers 12 and 13. Then, a wiring layer 90, which serves as an uppermost layer, and an insulation layer 91 (solder resist layer), which covers the wiring layer 90, are formed. Subsequently, as shown in FIG. 13(b), a dry film resist (DFR) 92, which is used for protection from sandblasting, is applied to the insulation layer 91. The DFR 92 is exposed and developed to form a predetermined pattern of openings 92a. Then, referring to FIG. 13(c), abrasive grains are blasted against the openings 92a of the DFR 92 to form openings 91a in the insulation layer 91 and expose parts of the wiring layer 90, which is the uppermost layer, as pads 90a or recognition marks 90b. Referring to FIG. 13(d), the DFR 92 is then removed.
Japanese Laid-Open Patent Publication Nos. 05-267802 and 2008-227309 disclose the prior art described above.